This invention relates to mobile communications and in particular to extension of a communications network having mobile subscribers, especially a PCN (Personal Communication Network), network to a PABX (Private Automatic Branch Exchange).
In Europe there are currently a number of different mobile communications standards which are incompatible with one another so that a mobile terminal designed for one system cannot be used with another. The Groupe Speciale Mobile (GSM) was set up in order to develop a single cellular standard for Europe. A GSM system network basically comprises a base-station system (BSS) which includes a base-station controller (BSC) and one or more basestation transceiver stations (BTS), a mobile-services switching centre (MSC), a home location register (HLR) and a visitors location register (VLR). Every subscriber (mobile station MS) is allocated to a home network, and possibly an MSC within that network, this being achieved by making an entry in the HLR. Whenever a mobile is switched on and at regular intervals thereafter, it will register with the system and give its location area (group of cells). If the mobile is not in its home area, the subscriber's data will be added to the visitor location register of the then local MSC. In the GSM system the MSC attends to the routing of a call to its destination, each MSC being connected to other MSCs, having interfaces for connection to PSTNs (Public Switched Telephone Networks such as BT or Mercury) and other services providers, and network management etc. functions.
Personal Communication Networks (PCN) now being developed in the UK are based on GSM standards but will operate at 1.8 GHz rather than the 900 MHz of the basic GSM standards. The PCN systems arose as a result of the UK Government's Department of Trade and Industry "Phone on the Move" document which was basically aimed at improvement to current mobile communications (cellular radio telephones). The latter are analogue and restricted in capacity due to the limited band of wavelengths currently available. As a result of the UK Government freeing a higher wavelength band, nominally 2 GHz, and the use of digital techniques, improved communications can be obtained. PCNs will not however be restricted to such mobile communications, but rather are intended to support communications to and from any standard radio or fixed telecommunication network and hence to provide a single communications network with a universal personal communicator, i.e. a truly personal portable telephone which permits communication at all times. Since the PCNs proposed are based on GSM standards they can include similar components to the GSM networks referred to above, or may include variants which are compatible with both GSM and PCN networks.